Process for pre-heating a hydro-fuel and producing in-situ steam for cooking

ABSTRACT

The present invention provides a process of cooking foods using a hydro-fuel to produce super heated in-situ steam. The hydro-fuel is propelled at a regulated flow rate into a pre-heating tube situated near a burner that is used in cooking, but also heats the tube. The pre-heating hydro-fuel is mixed with air in a mixing chamber to form a fuel-air mixture that is then transported to a burner tip on the burner. The fuel-air mixture is ignited at said burner tip to cause combustion producing the release of hot gases and in-situ steam that rise to cook food supported above said burner.

PRIORITY CLAIM

[0001] The present application claims benefit of U.S. Provisionalapplication No. 60/205598 filed on May 17, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to a cooking process and,more specifically, a process for pre-heating a hydro-fuel and using thefuel with a barbecue grill having a flaming or catalytic glowingcombustion mode that produces both heat and in-situ super-heated steamduring combustion of hydro-fuels. Hydro-fuels are relatively volatilealcohol or hydrocarbon liquid fuels containing miscible water orwater-in-oil micro-emulsions. The present invention relates tohydro-fuel cooking devices applicable for direct cooking of both meatand vegetables.

[0004] 2. Description of the Prior Art

[0005] With respect to barbecue grills, it is a common practice toprovide either gas or charcoal as a fuel source for the grill. Gas-firedbarbecue grills mainly use liquefied propane gas (LPG). Hot gases fromthe flames heat the food items that are placed directly on the foodsupport grid. In modem barbecue grills, non-combustible materials suchas lava stones are used as a heat transfer media for uniform heating offood items. In charcoal grills, radiation from the glow of the hot coalsheats the food item. The prior art contains extensive improvements inbarbecue grill designs including a variety of burner designs, heatdeflecting devices, surface cleaning strategies, and improvements tofood support systems. However, the present invention is novel in that itprovides a grill produces both heat and in-situ super-heated steamduring combustion of hydro-fuels fuels that is used in cooking foods.

[0006] The use of the hydro-fuel alcohol specifically as a traditionalfuel source in cooking stoves (or an indirect cooking device) is wellknown and is not reviewed here. A reference to the use of fuels otherthan common LPG gas or charcoal includes a solidified or semi-solidifiedalcohol. The U.S. Pat. No. 5,143,046 to Koziol teaches the use of gelledalcohol or a hydrocarbon type fuel in a barbecue grill. The methodologyresembles the common food warming method that uses gelled alcoholcommercially known as STERNO. The flame is diffusion type unlike the LPGpremixed flame generally utilized in barbecue grills. The fuelvaporization rate is adjusted by varying the heat-exposed area of thesolid fuel. In this surface combustion process, water, being the lessvolatile component, remains in the bottom of the gelled fuel reservoir.The present invention uses gasified premixed combustion and differs fromthis invention by bringing the water into the flaming region andproducing continuous super-heated steam.

[0007] The U.S. Pat. No. 5,189,945 to Hennick relates to a water-cooledbarbecue grill. Hennick teaches the use of circulating water from areservoir to cool the cooking surface to prevent food from sticking tothe surface. Food in the pans is cooked by heat from the water in thereservoir. The author claims the superiority of this barbecue grillbased on the moist cooking which reduces food from crumbling and leavesthe food tender. The present invention differs from Hennick in thatsuper-heated steam created during combustion of hydro-fuels is directlyapplied in cooking foods.

[0008] One important obstacle to overcome in using liquid fuel burnersis the problem of cold-starting the burning of the liquid fuel. Thisproblem occurs due to condensation of atomized liquid fuel inside thefuel-air premixing tube before the mixture reaches the burner tip beforethe initial ignition of fuel. However, once the burner system is warmenough, the mixture will usually vaporize and burn without any problem.Historically, several approaches have been reported to overcome thisproblem. These approaches include pre-heating the burner system withgelled alcohol (also called STERNO), a burning wick soaked in a liquidfuel, a fire starter, electrical pre-heaters and so on. The U.S. Pat.No. 5,080,580 to Clapp teaches a method of using a pressurized liquidfuel with a minor amount of hydrocarbon gas as a propellant. Thepropellant -air mixture is fed into the combustion chamber and ignitedeasily, followed by the main liquid fuel. This invention teaches a mucheasier and reproducible method of eliminating the cold-start problem.

SUMMARY OF THE INVENTION

[0009] This invention provides a novel process of grilling that solvesmany of the deficiencies in the prior art by utilizing combustion of anew class of fuel compositions, which contain miscible water referred toas “hydro-fuels.” A preferred embodiment uses fuel-grade ethanolcontaining a desired amount of water. Unlike petroleum products, ethanolis obtainable from renewable resources. The ethanol-water hydro-fuelproduces in-situ steam for direct cooking in barbecue grills.Alternatively, alcohol may be the selected hydro-fuel and isparticularly advantageous because of its low explosion hazard andstability in transport and storage. Unlike pressurized LPG, alcohol fuelis not pressurized during storage and transport, thus avoidingpressurized gas cylinders and increasing safety. The fuel tank ispressurized only before cooking. The absence of suffocating fumes andthe generally low danger level in case of accidental leakage of the fuelmakes the hydro-fuel user friendly.

[0010] More specific advantages of the present invention are provided bythe continuous steam produced from in-situ combustion. The in-situ steamprovides a moist cooking atmosphere, reduces cooking time, prevents foodfrom crumbling, leaves a cleaner grill surface, and adds taste andtenderness to the directly cooked food.

[0011] Combustion of hydro-fuels containing water produces heat as wellas steam. This steam is super-heated to flame temperatures. Along withconvective heat from hot gases, the steam directly contacts the fooditem placed on the grill. This invention provides ways to improve thecooking method by using a new fuel composition and conceptualmodifications designed to achieve the unique features indicated above.

[0012] Further, the present invention combines both heating andcontinuous steam generation in a single process, and thus eliminates theneed for a separate steam chamber. The steam is produced continuouslyand is applied uniformly to the surface of the food. The steam providesa controlled temperature environment and hence gives a better taste fordirectly heated food. Because of use of cleaner combustion products, themethod can be used for both indoor and outdoor cooking either inbarbecue grills or normal cooking as a stove.

[0013] Accordingly, a first object of this invention is to provide acooking device fueled by hydro-fuels that produces both heat and steamduring combustion in a gas-fired grill. Hydro-fuels are relativelyvolatile alcohols or hydrocarbon liquid fuels containing miscible wateror water-in-oil micro-emulsions. A preferred embodiment uses pressurizedfuel-grade ethanol containing a desired amount of water as a source offuel.

[0014] Another object is to retrofit a typical gas fired barbecue grillwith a liquid fired burner by installing a suitable pre-heating tube ora coil just above the burner rim. The pre-heating coil vaporizes theliquid fuel before it is injected into the mixing chamber. A provisionfor drainage of condensed liquid inside the mixing tube is provided.

[0015] Another object of the invention is to provide a cooking devicethat can be used for both indoor and outdoors cooking of meat andvegetable items. For example, ethanol, being an oxygenated fuel, bumscleaner than any other hydrocarbon fuel such as methane, ethane, propaneor butane. Hence, ethanol combustion is acceptable for indoor cooking.

[0016] Another object is to provide a cooking device that can be usedboth as a barbecue grill and a cooking stove. This objective can beachieved by using the cleaner burning ethanol, which is acceptable fordirect heating of food. Campers do not want to cook steaks, hamburgers,or hot dogs for every meal. Many foods, particularly breakfast foodssuch as oatmeal, eggs, and corn, and a variety of vegetable items tastebetter when cooked over direct heat from a stove. Thus, it is desirableto provide a portable outdoor cooking apparatus that is capable ofoperating as both a barbecue grill and a stove using a single burner.

[0017] Another object of the present invention is to provide a barbecuegrill that does not produce an open flame. A flameless combustionprocess may be achieved by inserting a catalytic wire mesh at thecombustion zone. In the presence of a combustion catalyst surface, theflaming reactions will be shifted to a glowing surface combustion. Theflame will completely disappear. This will reduce the chances ofaccidental fires. Catalytic combustion also provides cleaner combustionproducts. The heating is uniform because of infrared radiation.

[0018] Another object is to provide a barbecue grill with an option tocollect fat and other condensates produced, including condensed steamduring cooking. A concave plate is placed under the food support grid.The plate has a drip or a drain valve. Excess condensates that arecollected can be drained if desired.

[0019] Another objective is to provide a barbecue grill where thesurface remains relatively clean after cooking. Cleaning the grillsurface is always a problem because it tends to become encrusted withfood condensates, burner grease, and bits of food. Another problemassociated with barbecue cooking is that some food types tend to crumblewhen cooked on thin metal rods. Conventional barbecues do not provideany means for steam cooking of meat or vegetables.

[0020] Yet another object is to eliminate the cold start problemgenerally encountered in liquid fuel ignition. This problem occurs dueto condensation of atomized liquid fuel inside the fuel-air premixingtube before the mixture reaches the burner tip. However, once the burnersystem is warm enough, the mixture will usually vaporize and burnwithout any problem. The cold-start ignition problem is eliminated byfirst igniting the mixture inside the fuel-air mixing chamber, followedby an ignition at the burner tip.

[0021] These and other objects of the invention will be apparent tothose persons skilled in the art from the following detailed descriptionof a preferred embodiment of the invention.

BRIEF DESCRIPTION OF DRAWINGS

[0022]FIG. 1 is a schematic plan view of the present inventionillustrating the liquid fuel tank, hand pump, pre-heating tube and theburner assembly of hydro-fuel barbecue grill.

[0023]FIG.2a is a partial schematic perspective view of various parts ofthe hydro-fuel barbecue grill of the present invention.

[0024]FIG. 2b is a partial schematic plan view of various parts of thepresent invention including a flameless heating element.

[0025]FIG. 3 is a plan view of various parts of the present inventiondepicting fuel transfer by blowing air through a porous medium that issoaked with hydro-fuel.

[0026]FIG. 4 is a partial plan view of a pre-heating tube in the form ofa coil.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0027] Referring to the drawings, a process and apparatus for producingin-situ steam during combustion of hydro-fuels and its application todirect-heated cooking in a barbecue grill or an indirect cooking stoveis disclosed. In its preferred embodiment, the invention uses afuel-grade ethanol containing water as a liquid hydro-fuel pressurizedwith air. Any hydro-fuel having properties of combustion and stabilitysuitable for production heat and in-situ steam may be utilized by theinvention. Suitable hydro-fuels include alcohols such as methanol,ethanol, and propanol in either liquid or gelled form. Further,hydro-fuels include hydrocarbon liquid fuels containing miscible wateror water-in-oil microemulsions such as pentane, hexane, and octane.

[0028]FIG. 1 illustrates the liquid fuel storage tank 12, hand pump 14,pre-heating tube 20, fuel injection nozzle 22, and the burner system ofthe hydro-fuel grill. The liquid fuel is stored in the fuel tank 12,which has a refill-cap 16. A flow control valve 18 is provided at theoutlet of the fuel tank 12 to release and propel into the pre-heatingtube 20 a desired mass flow of the liquid fuel indicated by the arrows28 showing the flow of the liquid fuel. The fuel may be pressurizedusing a hand pump 14 that is shown built into the fuel tank 12.Alternatively, in place of a hand pump 14, the fuel tank 12 may bepressurized with secondary fuel gases such as butane or propane from anexternal source using an adapter, or non-combustible propellant gasessuch as N₂ or C0 ₂ gases could be used. Further, a pressurized cylindercould be especially adapted or an air compressed could be used to propelthe hydro-fuel flow into the pre-heating tube.

[0029] Upon release from the fuel tank 12, the fuel vapor 28 passesthrough a pre-heating tube 20 as shown in FIG. 1. The pre-heating tube20 may be a stainless steel or copper tube 20 or a coil (as in FIG. 4)placed just above the heat distribution source 32 such as a burner unitor flame holder. The function of the pre-heating tube 20 is not only totransport the fuel to the burner 32 but to vaporize the fuel beforeinjection using the heat from the burner flame. A fine nozzle 22produces a fuel jet creating a venturi action. Because of the lowpressure created by the accelerated flow through the nozzle 6, ambientair rushes into the system through the ventilation hole 34. Arrows 28show the flow of fuel in the pre-heating tube 20 and fuel-air mixtureinside a mixing tube 26. The mixture issues out of the tip of the burnertube 30 below the flame holder 32. Before the initial ignition, when thepre-heating 20 and the mixing tubes 26 are relatively cold, the liquidfuel often condenses and drops out of the tube 26 through the hole 34 asshown by 36. Therefore, the combustible fuel air mixture does not reachthe tip of the burner tube 10 and hence cannot be ignited at a typicallocation such as 14. This is usually referred as the cold-start problemwith liquid-fired burner systems. In order to overcome the cold-startproblem, the pre-heating tube and the burner tubes are usually heated byignition aids such as gelled alcohol (Sterno) or various types offire-starters. However, the present invention provides a new method toovercome the cold-start problem. The method involves a double ignitionapproach. The double ignition approach means igniting first at the fuelcondensing holes 34 located in the mixing tube 26. The mixture ignitesinside the premixing tube 26 producing a hissing sound. The flameusually terminates by itself, producing a hot fuel-air mixture thatpasses through the tip of the burner 30. The mixture is now ignited atthe burner tip 38. This process of double ignition is highlyreproducible and does not require any pre-ignition aids. The blue flamebecomes stable after a few seconds. Ignition can be achieved by an openpilot flame or a piezoelectric device attached to the system.

[0030] As illustrated in FIG.2, the premixed flame 40 is stabilized by aperforated flame holder or a bluff body 32. The premixed hydro-fuelvapor and air burn and produce steam at elevated temperatures. Thesuper-heated steam produced from the combustion of the hydro-fuel flowsupward along with hot gases, as shown by the upward arrows 44. Thehydro-fuel combustion yields well-controlled continuous steam or steamaerosol that contacts the food placed above the heat source. A metalgrid that functions as a food support 46 is placed above the flame, thevertical distance of which can be varied. A food item 48 is placed onthe food support 46. The in-situ steam 44 produced along with hot gascontacts the food item 48. The body of the barbecue grill may have anydesired shape.

[0031] An alternate embodiment includes a flameless glowing heatingelement 42 produced from the catalytic combustion of hydro-fuels. Inthis embodiment, the visible flame 40 is replaced by a catalyst surfacein the form of a mesh, a wire-plug, or a honeycomb structure as shown by42. A thin coating of the catalyst compound such as platinum, palladium,alloys of platinum and palladium, or transition metals is provided onthe substrate. In the presence of the catalyst, the gas phase combustionwill be shifted to surface combustion. The catalyst surface 42 startsglowing like a heating filament and radiates heat as seen inconventional charcoal grills. The flameless grill may be useful forindoor cooking where an open fire or a flame is not desirable. Moreover,the catalytic combustion yields cleaner combustion products. In additionto a hand pump 14, other variations are available for supplying theliquid fuel to the pre-heating tube 20. An electric mini-blower orpressurized propellant cartridges containing gases such as C0 ₂ and N₂may be utilized to transport the fuel to the pre-heating tube 20. FIG.3shows a schematic of an alternate fuel transport system in which thefuel from the tank 50 is transported into a tube containing a porousmedium 54 using a wick 56 or absorbing media which is inserted insidethe fuel tank 50. The liquid fuel is transported into to the porousmedium 54 by the capillary action. The porous medium 54 has an annularempty or a low porosity passage 58, through which air or the propellantgas from 60 passes through. The gas saturated with the liquid fuelenters the pre-heating coil 20. The flow is controlled by a controlvalve 62. The fuel tank has a fuel refill cap 52. The porous medium 54,as well as the wick 56, may consist of materials such as cotton,cellulose acetate, carbon cloth, and fiberglass. The mini-blower 60 maybe powered by re-chargeable batteries or other sources of power.

[0032]FIG. 4 shows an example of an alternative pre-heating tube 20 inthe form of a pre-heating coil 20. This coiled design provides increasedheat transfer area for the liquid fuel to be vaporized. Various otheradd-ons may be provided on the grill including a concave deflector atthe burner base for focusing heat onto the cooking area. A concave platemay be used to collect fat and meat constituents and re-generate smokefor adding flavor to food.

[0033] While the present invention has been particularly shown anddescribed with reference to an embodiment thereof, it will be understoodby those skilled in the art that various changes in form and detail maybe made without departing from the spirit and scope of the presentinvention.

I claim:
 1. A process of cooking foods comprising the following steps:a. providing a source of a hydro-fuel; b. propelling a regulated flow ofthe hydro-fuel into a pre-heating tube situated near a burner; c.pre-heating the hydro-fuel; d. mixing the hydro-fuel with air in amixing chamber to form a fuel-air mixture; e. transporting the fuel-airmixture to a burner tip on said burner; f. igniting the fuel-air mixtureat said burner tip to cause combustion producing the release of hotgases and in-situ steam that rise to cook food supported above saidburner.
 2. A process of cooking foods as claimed in claim 1 includingthe interim step of igniting the fuel-air mixture in the mixing chamberto provide for cold start ignition of the fuel-air mixture prior toigniting the fuel-air mixture
 3. A process of cooking foods as claimedin claim 2 in which ignition of the fuel-air mixture in the mixingchamber is accomplished using an open pilot flame or piezoelectricdevice.
 4. A process of cooking foods as claimed in claim 1 in whichsaid hydro-fuel is an alcohol.
 5. A process of cooking foods as claimedin claim 4 in which said alcohol is an ethanol.
 6. A process of cookingfoods as claimed in claim 1 in which said hydro-fuel is a hydrocarboncontaining miscible water or water-in-oil microemulsion.
 7. A process ofcooking foods as claimed in claim 1 in which said regulated flow of thehydro-fuel into a pre-heating tube is propelled by air pressure causedby using a hand pump.
 8. A process of cooking foods as claimed in claim1 in which said regulated flow of the hydro-fuel into a pre-heating tubeis propelled by air pressure provided by adapting the pre-heating tubeto said source of hydro-fuel which includes a pressurized cylinder.
 9. Aprocess of cooking foods as claimed in claim 1 in which said regulatedflow of the hydro-fuel into a pre-heating tube is propelled by airpressure provided by a compressed air cylinder adapted to said source ofhydro-fuel.
 10. A process of cooking foods as claimed in claim 1 inwhich said regulated flow of the hydro-fuel into a pre-heating tube ispropelled by a non-combustible gas
 11. A process of cooking foods asclaimed in claim 1 in which said regulated flow of the hydro-fuel into apre-heating tube is propelled by the capillary action of a media capableof absorbing hydro-fuel.
 12. A process of cooking foods as claimed inclaim 1 in which a venturi is used to cause a flow of air into themixing chamber for mixing the hydro-fuel with air in a mixing chamber toform a fuel-air mixture.